Hafler 1K trimpot fried - how do I replace?

HaflerFreak · 14th August 2007, 10:03 AM

I have recently refreshed/restored my Hafler XL-280 power amp and upon powering up with a series lightbulb and a variac, I noticed that the bias trimpot on one side appeared to be very erratic in its operation. After some fiddling, I powered down and gave the trimpot 10-15 turns from stop to stop to loosen it up and clean the contacts.
When I turned the amp back on the bias was very, very low (about 50mA at full ine voltage) and the trimpot did absolutely nothing no matter how mutch I turned it. I assume the trimpot is fried - the bias was almost 200mA at 60 volts AC before I tried to loosen it up - that was too high, now it's stuck low...

When I looked on digikey and Mouser, I found nothing. This is a 1000 Ohm single turn / side adjust with a 10mm spacing between the legs. I think the wiper is 5mm offset to the rear. Everything I find is 5mm spacing with 2.5mm offset.

Anyone have any suggestions? Is wirewound Ok or only Cermet?

Anyone want to sell a Hafler 1K trimpot?

EchoWars · 14th August 2007, 10:55 AM

Wish I could see, but I suspect that you're not being creative enough.

If the holes are too far apart, I've occasionally lengthened the leads on the trimpot with leads cut from a resistor.

Use your noggin. Shouldn't be too tough to come up with a fix.

unclejed613 · 14th August 2007, 12:09 PM

wirewound=bad idea..... wirewounds have a "jumpy" response, and the resistance changes in steps. you want a pot with a smooth response and continuously variable for a bias pot

14th August 2007, 10:03 AM	#1
HaflerFreak diyAudio Member Join Date: Jun 2007 Location: Westmont, IL	Hafler 1K trimpot fried - how do I replace? I have recently refreshed/restored my Hafler XL-280 power amp and upon powering up with a series lightbulb and a variac, I noticed that the bias trimpot on one side appeared to be very erratic in its operation. After some fiddling, I powered down and gave the trimpot 10-15 turns from stop to stop to loosen it up and clean the contacts. When I turned the amp back on the bias was very, very low (about 50mA at full ine voltage) and the trimpot did absolutely nothing no matter how mutch I turned it. I assume the trimpot is fried - the bias was almost 200mA at 60 volts AC before I tried to loosen it up - that was too high, now it's stuck low... When I looked on digikey and Mouser, I found nothing. This is a 1000 Ohm single turn / side adjust with a 10mm spacing between the legs. I think the wiper is 5mm offset to the rear. Everything I find is 5mm spacing with 2.5mm offset. Anyone have any suggestions? Is wirewound Ok or only Cermet? Anyone want to sell a Hafler 1K trimpot?

14th August 2007, 12:09 PM	#3
unclejed613 diyAudio Member Join Date: Dec 2006	wirewound=bad idea..... wirewounds have a "jumpy" response, and the resistance changes in steps. you want a pot with a smooth response and continuously variable for a bias pot __________________ Vintage Audio and Pro-Audio repair ampz(removethis)@sohonet.net spammer trap: http://www1284177414881.v-dc.net/

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
How to create a DC offset trimpot?	reiver	Solid State	13	15th June 2008 01:38 PM
1k 1/4W trimpot old style hafler	eyoung	Swap Meet	0	1st December 2007 12:37 AM
Lesson learned - fried my Hafler - what went wrong?	HaflerFreak	Solid State	5	15th August 2007 02:39 AM
4 gang pot / trimpot needed	deandob	Swap Meet	1	26th April 2005 11:52 PM
ZEN question inputImpedance Trimpot etc	Smithers	Pass Labs	5	4th April 2003 02:09 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

14th August 2007, 10:55 AM	#2
EchoWars diyAudio Member Join Date: Dec 2002 Location: Left of the Dial	Wish I could see, but I suspect that you're not being creative enough. If the holes are too far apart, I've occasionally lengthened the leads on the trimpot with leads cut from a resistor. Use your noggin. Shouldn't be too tough to come up with a fix.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)